Immunoassay, which takes advantage of natural immunological reactions, is a well-recognized technique in quantifying biological analytes that are present in biological fluids. Such analytes include, but are not limited to, antigens, antibodies, therapeutic drugs, narcotics, enzymes, hormones and proteins. In many instances immunoassay has made possible the detection of biological compounds that are present in trace quantities too low for traditional chemical and enzymatic techniques.
The most commonly known immunoassay techniques provide for a determination of the presence and/or concentration of either a specific antigen, a specific antibody or a specific antigen/antibody complex. For example, given a known amount of antibody or antigen, the level of its corresponding antigen or antibody can be determined. When the concentration of antibody or antigen is too small for direct measurement, a label can be affixed to a known fraction of the antibody or antigen. This label, which is present and measurable at the requisite concentration, acts as a marker for the extent of antibody/antigen binding between the unknown antibody or antigen and its complementary antigen or antibody. The distribution of label between the bound and unbound antibody or antigen can then be used to calculate the amount of unknown that was present in the liquid sample.
In an alternative type of immunological assay commonly referred to as a sandwich assay, an antibody is contacted with a sample containing an analyte to cause the analyte to bind to the antibody. This complex is then contacted with a solution of a labeled antibody which reacts with the bound analyte. The amount of bound labeled antibody is directly proportional to the amount of bound analyte.
Devices useful in testing samples containing antibodies are known and examples are disclosed in U.S. Pat. No. 5,591,645, U.S. Pat. No. 4,632,901 and U.S. Pat. No. 4,483,925 all of which are incorporated by reference herein. Currently, antibody containing samples can be tested singly against many different antigens by setting up individual assays in plates. Alternatively, many antibodies can be tested against single antigens using plates with that antigen attached. Single samples can be tested rapidly using membrane based devices.
What is still lacking in the art, however, is a means for incorporating the simple, rapid membrane-based immunoassay techniques with the large sample techniques of microplate assay systems.